Arched mine gallery support and beam therefor



Feb. 9, 1965 E. BLENKLE ETAL 3,168,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR 5 Sheets-Sheet 1 FiledAug. 17, 1959 INVENTORS w ee/ml W su Ms W,

Fig. 2

Feb. 9, 1965 BLENKLE ETAL 3,168,315

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR Filed Aug. 17, 1959 5Sheets-Sheet 2 Feb. 9, 1965 Filed Aug. 17. 1959 E. BLENKLE ETAL3,168,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR 5 Sheets-Sheet 5 INVENTOR$H 4 QM Mi '4, M W S ML am Feb. 9, 1965 E. BLENKLE ETAL 3,163,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR Filed Aug. 17, 1959 5Sheets-Sheet 4 x INVENTOR'S Wi 2w,

1965 E. BLENKLE ETAL 3,168,815

ARCHED MINE GALLERY SUPPORT AND BEAM THEREFOR Filed Aug. 17, 1959 5Sheets-Sheet 5 a INVENTOR5 w W21 Fig. 6 W M WKWM United States Patent3,168,815 ARCHED MENE GALLERY SUPPORT AND BEAM THEREFGR Erwin Elenkieand Rudolf Seiz, Bochum, Germany, assignors, by mesne assignments, toBochumer Eisenhutte Heintzmann & C0., Bochum, Germany Filed Aug. 17,1959, Ser. No. 834,250 r Claims priority, application Austria, Aug. 16,1953, A 5,735/58 Claims. (Cl. 61-45) For the supports of mine galleries,use is frequently made of trough-shaped support sections in a form afterthe style of a structural iron, which are connected together to formannular or arch-shaped support frames. With this type of support knownas a sliding arch support the mutually congruent sections are placedwith their ends co-directionally one inside the other and in the regionof the overlap are clamped in such manner that when a determined rockpressure is exceeded they can slide axially in relation to one another,so that the support acquires the desired resilience.

These trough sections usually have a trapezoidal crosssection such thatthe webs disposed at a distance from one another and diverging towardsthe flanges are connected by a base part. The webs may be bounded eitherby substantially plane or curved surfaces so that they enclose betweenthem an aperture angle which is either substantially constant or whichdecreases towards the flanges. This aperture angle is preferably betweenabout 15 to 45. The base part connecting the spaced apart webs is inmost cases of substantially plane construction. However, trough sectionsare also known which have a base part which is curved concavely towardsthe flanges and which merges, still with curvature, into the sectionwebs. The shape and dimensions of the flanges, webs and base parts andhence the material distribution over the section cross-section are inmost cases so selected that the moments of resistance in the two majoraxes are approximately equal or at least close to one another in suchmanner that they do not differ from one another by more than about 50%.

In the known trough-shaped mine support sections the section webs areconnected by the section base at their lower edge remote from thesection flanges. This section base usually has a wall thickness which islarger than the section webs, since on the bending of the sections andon the longitudinal displacement of the sections under the action of therock pressure, for example, it is exposed to considerable bending andtorsional stresses. The accumulation of material resulting from thereinforced construction of the section base must be equalized by acorrespondingly intensive accumulation of material in the region of thesection flanges and the upper part of the webs, in order to keep themass centre approximately at half the section height and to maintain thelargest possible moment of resistance in the X-axis. An accumulation ofmaterial of this kind in the region of the section flanges has thedisadvantage, however, that on the bending of the sections relativelylarge opening-up forces occur which are a function of the massesdisposed in the region of the edge zone, so that the webs have to bemade relatively thick and can be given only a relatively slightinclination.

A trough section is also known, which has a curved section base which isdimensioned to be particularly thick and which to reduce the massesdisposed in this region is provided with lateral recesses which enclosebetween them a thick middle rib. Since the recesses are disposed in theregion of the transition of the section base to the section on thebending of the sections under the action of the rock pressure and theirrelative displacement particularly ddhbfii Patented Feb. 9, 1%65intensive stresses occur, they can be given only limited dimensions, sothat in order to obtain a uniform mass distribution the section flangeshave to be given a thick construction. Such an accumulation of materialin the region of the section flanges, in conjunction with theconsiderable angle of inclination of the section webs, however, resultsin considerable openingup forces on the bending of the sections, so thatthe webs also have to be made very strong.

In comparison with these previously known troughshaped mine supportsections, according to the invention an improvement is achieved bydisposing the section base at a distance which preferably exceeds itsthickness but which is dimensioned to be less than half the sectionheight, above the lower longitudinal edge of the section webs which isremote from the flanges. In these circumstances, it has provedparticularly advantageous to make the distance of the section base fromthe lower web edge approximately equal to onethird to one-sixth of thesection height.

In consequence of the fact that in the set of troughshaped mine supportsections proposed according to the invention the section webs areconnected by the section base, not at their lower end as in the known.sections, but in a middle region disposed preferably below half the webheight, the mass centre or centre of gravity is shifted towards theflanges, that is to say in the upward direction. In consequence of thisshift of the centre of gravity, the section flanges may be given aconsiderably lighter construction in comparison with the known forms ofsection. This reduction of masses in the region of the flanges has theadvantage that the opening-up forces occurring on bending and on therelative displacement of the sections is considerably reduced. Aparticular advantage of the invention, however, is that as a result ofthe raising of the section base the distance from the section flangesand hence the ettective lever arm of the opening-up forces areconsiderably reduced, so that the bending stresses occurring in thesection webs on the bending of the sections are reduced by aconsiderable degree in comparison with the previously known forms ofsections. Thus, for example, given otherwise identical sectionconstruction, by reducing the section flanges and disposing the sectionbase at a distance corresponding approximately to one-quarter toone-fifth of the section height above the lower web edges it is possibleto reduce by 60 to the bending stresses occurring on bending in thesection webs. The consequence of this is that given the same resistanceof the sections to opening up, the section webs can be made considerablythinner, or that given equally thick construction of the webs thesections have a many times higher resistance to opening up. Since themagnitude of the opening-up forces occurring on bending is dependent,not only on the masses, but also on the strength properties in theregion of the edge zones and on the aperture angle of the section webs,it is immediately possible to give the section webs a greaterinclination or to temper the sections to a considerably higher degreethan was possible with the forms of sections known heretofore. Inconsequence of the fact that the section webs and the section flangescan be made considerably thinner than hitherto owing to the morefavourable mass distribution and the lower bending stresses occurringduring bending, it is further possible to use steels of a lower gradefor the rolling of the sections, that is to say, steels having lessresistance to ageing (for example rimmed steels), since with such smallwall thicknesses the cooling of the rolled sections proceeds so rapidlythat there is no fear of any impermissible ageing phenomena.

In addition to a considerably greater cross-sectional stability, thetrough section proposed according to the invention also has a bettertorsional stiffness, this being of r Z3 considerable importance inconsequence of the frequently varying stresses of the sections bytherock pressure, these stresses constantly chan ing their nature.

The reduced distance between the section base and the mass centrefurther has the consequence that a reinforcement of the section base hasonly a minor effect on the mass distribution so that the section basecan immediately be made of a thickness such as is required for thepurposes of the forces transmitted to the section base at any giventime.

In every case, however, it is advisable to adapt the distance betweenthe section base and the lower longitudinal edges of the section websand the shape and dimensions of the flanges, webs and base part to oneanother in such manner that the mass centre is disposed approximately athalf the section height. The construction of the flanges,

ebs and base part in the individual case, may, of course, differ greatlyso that the guiding principle of the invention can be embodied innumerous forms of construction.

As a rule it is advantageous for the section webs to have beneath thesection base a wall thickness which on the average is considerablygreater than above the section base. This not only enables the sectionbase to be disposed at a particularly great distance above the lowerlongitudinal edge of tie ection webs, while retaining a favourable massdistribution, but another advantage obtained is great cross-sectionalstability of the Web parts disposed beneath the section base, so that onthe bending of the sections under the action of the rock pressure noimpermissible deformations of these web parts disposed beneath thesection base need be feared.

In these cir cumstances the wall thickness of the part of the websdisposed beneath the section base advantageously increases towards thebase preferably conically, so that in the transitional region subjectedto the greatest stresses between the webs and the section base thegreatest cross secion is available. The mutually facing wall surfaces ofthe web parts disposed beneath the section base are advantageouslyinclined to one another at a downwardly open small angle of, forexample, about 6 to With such an aperture angle the lower web parts canalso be rolled without difficulty, and in addition, even in the event ofa' considerable distance between the section base and the lower webedge, the web cross-section does not become excessively large in theregion of the transition to the section base. The part of the sectionwebs disposed above the section base ma on the other hand, as a role begiven a wall thickness which on the average is considerably less thanthe section base.

In one advantageous embodiment, the shape and dimensions of the sectionflanges, section webs and section bases are adapted to one another insuch manner that the overlapping scction ends touch one another onlybetween the lower web edges of the inner section and the section base ofthe outer section. This gives the possibility of concentrating on asmall region the frictional forces transmitted on the relativedisplacement of the sections, while in particular the parts lying abovethe section base are kept quite free of frictional stresses occurring onthe relative displacement, and can be given correspondingly small wallthicknesses. This arrangement of the sections further has the advantagethat during rolling inevitable production tolerances have no effect inpractice on the magnitude of the contact surfaces between the sections,so that in contrast to the friction-closure hitherto usually employedpractically constant friction conditions are obtained in all cases overa relatively large part of the section. The concentration of thefriction on such small contact surfaces further affords the advantagethat given appropriate tightening of the clamping connections it isimmediately possible to obtain a surface pressure which liesconsiderably above the permissible surface pressure and with whichparticularly favourable friction conditions are obtained. With such highsurface pressures, as tests have shown, no seizure occurs at the contactsurfaces sliding one upon the other, but a certain material displacemcntoccurs in the region of the contact surfaces, and this has the resultthat independently of the magnitude of the clamping force applied at anygiven time a substantially constant frictional resistance is obtainedbetween the sections.

A number of exemplified embodiments of the invention are illustrated inthe drawing, in which:

FIGURE 1 is an elevation of a gallery support frame,

FIGURE 2 is a section on the line IIII on a larger scale,

FIGURE 3 is a cross-section through the trough sec tions disposedco-directionally one inside the other, as shown in FIGURE 2, on a largerscale,

FIGURE 4 is another embodiment of trough sections, likewise incross-section,

FIGURE 5 is a cross-section through a third embodiment oftrough-sections disposed co-directionally one inside the other, 7

FIGURE 6 is a fourth embodiment, likewise in crosssection.

In the arch-shaped gallery support shown in FIGURE 1, the side segments1 consisting of trough sections are resiliently clamped by clampingconnections 3 to the roof segment 2 of arch-shapedconstruction. The roofsegment 2 is fitted by its ends co-directionally into the end parts ofthe side segments 1, while the clamping means 3 are disposed in theregion of the overlap of the sections 1, 2. The clamping connections 3are provided in known manner with coupling projections which engage overthe ends of the roof segment 2-, in such manner that V on a relativedisplacement of the support segments 1, 2 under the action of the rockpressure the clamping connections 3 are driven by the ends of the roofsegment 2.

As will be apparent from FIGURES 2 to 5, the outer section I and theinner section 2 have a congruent crosssection, so that the sections canbe placed one inside the other in any desired manner or roof and sidesegments can be made from the same section bars.

All the exemplified embodiments illustrated in the drawing show troughsections having a substantially trapezoidal cross-section. In thedrawings, the section flanges. are denoted by reference 5, the sectionwebs by 6 and the section base by 7. In all cases, the section base 7 isdisposed above the lower longitudinal edge 8 of the section webs 6 at adistance g which exceeds its wall thickness b by a considerable amount.In the exemplified embodiments illustrated in the drawing, the distancea corresponds approximately to one-fourth to'one-fifth of the sectionheight h. The section webs 6 are divided by the section base 7approximately in the ratio of 1:3 into an u per part do and a lower part6b. The parts 6b of the Webs disposed beneath the section base 7 have awall thickness which onthe average is considerably greater than the webparts 6a disposed above the section base 7. The average wall thicknessof the upper parts 64 of the section webs is in addition considerablyless than the thicke ness b of the section base 7.

While the lower longitudinal edge 8 of the section webs 6 is of roundedconstruction, the wall thickness of the web parts 6b increases conicallytowards the section base 7. The average wall thickness of the sectionparts 6b corresponds in these circumstances to approximately thethickness 12 of the section base 7. The mutually facing wall surfaces ofthe web parts 6b are inclined to one another at a downwardly open smallangle a, which in the different exemplified embodiments illustrated inthe drawing lies between about 6 and 10.

The outer surfaces of the section webs 6 diverging towards the sectionflanges 5, in the embodiments shown in FIGURES 3 and 5, are formed byoutwardly convex surfaces, whichare curved according to a large radiusof curvature and which are adjoined by the outwardly projecting sectionflanges 5. In the embodiments shown in FIGURES 3 and 5 the sectionflanges 5 have a height 0 stresses.

which exceeds by a considerable amount the thickness 12 of the sectionbase 7. The inner walls of the parts 6a of the section webs disposedabove the section base 7 are likewise bounded by outwardly convexlycurved surfaces having a large radius of curvature, so that the webparts 6a have a slightly curved cross-section tapering conically towardsthe flanges 5. The aperture angle 5 enclosed by the mutually facing wallsurfaces of the upper web parts 6a decreases from about 28 to 22 fromthe section base 7 towards the flanges 5.

In the exemplified embodiment shown in FIGURE 4, the outer surfaces ofthe webs 6, which surfaces are remote from one another, are formed eachby two plane surfaces inclined to one another by small angle. In similarmanner the mutually facing insides of the upper web parts 6a are boundedby in each case two plane surfaces inclined to one another by a smallangle. In consequence, in the exemplified embodiment shown in FIG- URE 4as well, the aperture angle 8 enclosedby the inner walls of the upperweb parts 6a is smaller in the region of the section flanges 5 than justabove the section base 7. Similarly, the wall thickness of the upper webparts 6a decreases from the section base '7 towards the flanges 5. Theheight of the section flanges in the embodiment shown in FIGURE 4 issmaller than the thickness b of the section base 7. On the other hand,they have a considerably greater width d in comparison with theirheight.

In the embodiment shown in FIGURE 5, the section base '7 has adownwardly projecting rib-shaped reinforcement 9 disposed between thesection webs 6. The ribshaped reinforcement 9 is disposed symmetricallyto the Y-axis of the section and has a wall thickness which increasesconically towards the section base and which corresponds approximatelyto the wall thickness of the lower web parts 612. The lower longitudinaledge of the rib 9 provided on the section base 7 is of roundedconstruction and is disposed in the same plane as the lower longitudinaledges of the section webs 6. It is, however, naturally possible to givethe rib-shaped reinforcement 9 a different shape or different dimensionsif required than is the ease in the exemplified embodiment shown in FIG-URE 5. In some cases it is possible to provide more than one reinforcingrib 9 between the lower web parts 612.

The section base 7 is considerably reinforced by the middle rib 9 sothat the said base in consequence of the shortening of the lever arms asa result of the middle rib 9 is able to take substantially greaterbending and torsional In addition, additional accumulation of materialbeneath the section base 7 gives the possibility of disposing thesection base 7 at a particularly high level and hence makingparticularly small the effective lever arm for the opening-up forces,that is to say the distance from the section flanges 5.

In the embodiments shown in FIGURES 2, 3, and 4, the section endsdisposed co-directionally one inside the other are supported in theregion of the overlap only between the lower longitudinal edges 8 of thesection webs of the inner section 2 and the section base 7 of the outersection. The flanges 5 and the mutually facing surfaces of the sectionwebs of the inner and outer sections on the other band do not touch. Inthe form of section shown in FIGURE 5, the section ends overlapping oneanother are additionally supported against the base 7 of the outersection 1 by the rib-shaped reinforcement 9 of the inner section 2.However, in this case as well, the outer and inner sections do not toucheither between the flanges 5 or between the webs 6.

Since the lower longitudinal edges 8 and 10 of the sections webs 6 andof the centre rib 9 are in addition of circular construction, such smallcontact surfaces are obtained between the inner and outer sections thateven in the case of normal tightening of the clamping connections 3 thesurface pressure transmitted by the longitudinal edges 8 of the innersection webs to the base of the outer section exceeds the permissiblesurface pressure so that on the relative displacement of the sectionsthere is no seizure, but, with small material displacements in theregion of the small surface zones supported against one another, asliding with practically constant frictional resistance.

The principle of the invention can naturally also be applied to thosesections which are supported against one another additionally by thewebs and/or the flanges or only by the webs and/ or the flanges. Thus,for example, FIGURE 6 shows an embodiment in which the sections 1, 2 aresupported against one another by the flanges 5 and in addition by thewebs 6, while a gap remains between the lower longitudinal edges 8 ofthe inner section webs and the base 7 of the outer section 2.

FIGURE 2 shows an advantageous embodiment of a clamping connection 3 forthose sections which are supported only between the lower web edges 8 ofthe inner section 2 and the base 7 of the outer section or, if required,additionally by way of a rib-shaped reinforcement 9 of the innersection. The clamping connection consists of two fiat-iron sections 11,12, which are bent to correspond to the. section shape and which areclamped together by clamping screws 13. In this case, an arrangement ismadesuch that the halvesll, 12 of the clamping connection are subjectedsubstantially to tensile stress. The up per part 11 of theclampingconnection is of U-shape to correspond to the distance'between thesection flanges 5 in such manner that both the flanges of the innersection 2 and the flanges of the outer section 1 are guided between theside parts 11a. In this way, in spite of the small contact surfacesbetween the sections 1, 2 placed one inside the other, good guidance isobtained with the relative displacement occurring under the action ofthe rock pressure. Moreover, this construction of the clamping stirrupparts 11, 12 gives the effect that the webs of the support sections 1, 2undergo no bending stresses at all or no appreciable bending stresses.As is apparent from FIGURE 2, the outer section 1 is likewise supportedonly by the lower longitudinal edges 8 of the section webs against thebase 12a of the clamping stirrup lower part 12, so that even betweenthese contact surfaces a surface pressure is obtained which lies abovethe permissible surface pressure.

We claim:

I. A rolled beam adapted to nest in overlapping relation with at leastone similar beam to form at least part of a mine gallery support, saidbeam comprising a pair of oppositely inclined side walls symmetricallyarranged with respect to a longitudinal plane of symmetry and having apair of outer longitudinal edge portions spaced farther from each otherthan a pair of inner longitudinal edge portions thereof, and atransverse web integral with and extending between said side wallssubstantially normal to said plane of symmetry and forming the onlyconnection between said side walls, said web being spaced from said pairof inner edge portions a distance which on the one hand is greater thanthe thickness of said web and which on the other hand is smaller thanhalf the distance of said pair of outer edge portions from said pair ofinner edge portions so that said web forms with said side walls a deepand a shallow longitudinal channel separated by said web, the widthbetween the inner faces of said side walls defining said deep channeland measured normal to said plane of symmetry at any distance from theweb surface of the deep channel being greater than the width between theouter faces of said side walls measured normal to said plane of symmetryat the same respective distance used for the first-mentioned width butfrom said inner edge portions of said beam, whereby when one of saidbeams is nested into the deep channel of another beam the nested beamwill only be supported on said web in said deep channel of said otherbeam, with the outer faces of the side Walls of said nested beam spacedfrom the inner faces of said deep channel of the other beam.

2. A beam as recited in claim 1, and wherein the distance between saidweb and said inner edge portions is between one-third and one-sixth ofthe distance between said inner and outer edge portions.

3. A beam as recited in claim 1, and wherein each side wall has athickness which tapers from said web toward the inner edge portion ofthe side wall.

4. A beam as recited in claim 1, and wherein the thickness of each sidewall is greater at the portion thereof extending from said web towardthe inner edge portion than at the portion thereof extending from theweb toward the outer-edge portion. 7

5. A beam as recited in claim 1, and wherein said web has integrallyformed therewith a longitudinal rib located between and spaced from saidside walls and having a cross section which tapers from said Web towardthe edge of said rib distant therefrom.

6. A beamasrecited in claim 1, and wherein said web has opposed fiatfaces parallel'to each other.

7. A beam as recited in claim 1, and wherein the portions of said. sidewalls which extend between said web and the outer edge portions divergefrom each other adjacent said web to a greater degree than adjacent saidouter edge portions.

81A beam as recited in claim 1, and wherein said side walls respectivelyhave outwardly directed flanges at the edges of said side walls whichare located at said outer longitudinal edge portions, and said webhaving a thickness greater than the thickness of each side wall intheregion of said flange thereof.

9. A beam as recited in claim 8, and wherein said flanges also arethicker than the thickness of said side walls in the regions of saidflanges, respectively.

10. In an arched mine gallery support, in combination, two substantiallycongruent trough-shaped beams, an end portion of one beam being nestedin overlapping relationship in the end portion of the other beam andsaid beams being and yieldably connected at said end portions forsliding movement relative to each other, each of said beams comprising apair of oppositely inclined side walls symmetrically arranged withrespect to a longitudinal plane of symmetry and having a pair of outerlongitudinal edge portions spaced farther from each other than a pair ofinner longitudinal edge portions thereof, and a transverse web integralwith and extending between said side walls substantially normal to saidplane of symmetry and being spaced from said pair of inner edge portionsa distance which, on the one hand, .is greater than the thickness ofsaid web and which, on the other hand,

is smaller than half the distance of said pair of outer edge portionsfrom said pair of inner edge portions so that said web forms with saidside walls a deep and a shallow longitudinal channel separated by saidweb, the width between the inner faces of the side walls defining thedeep channel and measured normal to said plane of symmetry at anydistance from the web surface of the deep channel being greater than thewidth between the outer faces of the side walls measured normal to theplane of symmetry at the same respective distance used for thefirst-mentioned width but from the inner edge portions of said beam,said nested beam being supported on said web in said deep channel ofsaid other beam, with the outer faces of the side walls of said nestedbeam spaced from the inner faces of said deep channel of the other beam.

11. In a mine gallery support as set forth in claim 10, wherein thedistance of said transverse web from said inner edge portions is betweenone-third and one-sixth of the distance between said outer and saidinner pair-of edge portions.

12. In a mine gallery support as set forth in claim 10, in which themean wall thickness of the side wall por tionsbetween said transverseweb and said pair of inner edge portions is greater than the meanthickness of the side wall portions between said transverse web and saidouter edge portions, and said thickness of the side wall portionsbetween said transverse web and said pair of inner edge portions tapersfrom said web toward said inner edge portions.

13. In a mine gallery support as set forth in claim 10, in which each ofsaid beams includes a longitudinal rib integral with said web andprojecting therefrom into the space between said pair of inner edgeportions and in which the thickness of said rib tapers from said webtoward the free edge thereof.

14. in a mine gallery support as set forth in claim 13,.

in which said free edge of said rib is located in a plane substantiallynormal to the plane of symmetryand'passing through said pair of inneredge portions.

15. In a mine gallery support as set forth in claim 14, in which saidset of beams engage each other at said nested end portions thereof onlyalong the inner edge portions and said free edge of said rib of one beamand the web of the other beam.

References Cited in the file of this patent UNITED STATES PATENTS2,713,774 Heintzmann July 26, 1955 FORElGN PATENTS 412,561 Great BritainJune 25, 1934 487,826 Great Britain June 27, 1938 697,260 Great BritainSept. 16, 1953 700,020 Great Britain Nov. 25, 1953 962,879 Germany May2, 1957 1,034,777 France Apr. 15, 1953 1,196,069 France May 25, 19591,042,997 France June 10, 1953 OTHER REFERENCES German patentapplication B 37691 VI/5c; June 14, 1956, K1. 5c, Gruppe 9/10.

'German patent application 1,003,159, February 28, 1957 (K1. 5c 9/10).

German patent application 1,009,133, May 29, 1957 (K1. 5c, Gruppe 9/10).

10. IN AN ARCHED MINE GALLERY SUPPORT, IN COMBINATION, TWO SUBSTANTIALLYCONGRUENT TROUGH-SHAPED BEAMS, AN END PORTION OF ONE BEAM BEING NESTEDIN OVERLAPPING RELATIONSHIP IN THE END PORTION OF THE OTHER BEAM ANDSAID BEAMS BEING AND YIELDABLY CONNECTED AT SAID END PORTIONS FORSLIDING MOVEMENT RELATIVE TO EACH OTHER, EACH OF SAID BEAMS COMPRISING APAIR OF OPPOSITELY INCLINED SIDE WALLS SYMMETRICALLY ARRANGED WITHRESPECT TO A LONGITUDINAL PLANE OF SYMMETRY AND HAVING A PAIR OF OUTERLONGITUDINAL EDGE PORTIONS SPACED FARTHER FROM EACH OTHER THAN A PAIR OFINNER LONGITUDINAL EDGE PORTIONS THEREOF, AND A PAIR OF INNERLONGITUDINAL EDGE PORTIONS THEREOF, SAID SIDE WALLS SUBSTANTIALLY NORMALTO SAID PLANE OF SYMMETRY AND BEING SPACED FROM SAID PAIR OF INNER EDGEPORTIONS A DISTANCE WHICH, ON THE HAND, IS GREATER THAN THE THICKNESS OFSAID WEB AND WHICH, ON THE OTHER HAND, IS SMALLER THAN HALF THE DISTANCEOF SAID PAIR OF OUTER EDGE PORTIONS FROM SAID PAIR OF INNER EDGEPORTIONS SO THAT SAID WEB FORMS WITH SAID SIDE WALLS A DEEP AND ASHALLOW LONGITUDINAL CHANNEL SEPARATED BY SAID WEB, THE WIDTH BETWEENTHE INNER FACES OF THE SIDE WALLS DEFINING THE DEEP CHANNEL AND MEASUREDNORMAL TO SAID PLANE OF SYMMETRY AT ANY DISTANCE FROM THE WEB SURFACE OFTHE DEEP CHANNEL BEING GREATER THAN THE WIDTH BETWEEN THE OUTER FACES OFTHE SIDE WALS MEASURED NORMAL TO THE PLANE OF SYMMETRY AT THE SAMERESPECTIVE DISTANCE USED FOR THE FIRST-MENTIONED WIDTH BUT FROM THEINNER EDGE PORTIONS OF SAID BEAM, SAID NESTED BEAM BEING SUPPORTED ONSAID WEB IN SAID DEEP CHANNEL OF SAID OTHER BEAM, WITH THE OUTER FACESOF THE SIDE WALLS OF SAID NESTED BEAM SPACED FROM THE INNER FACES OFSAID DEEP CHANNEL OF THE OTHER BEAM.